The present application is based on Japanese Patent Application No. 2001-307749, which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to a laminated quarter-wave plate or a circularly polarizing plate adapted to compensation for birefringence, a liquid-crystal display device using the same and a method for producing the same.
2. Description of the Related Art
As a wave plate capable of providing a retardation of a quarter wavelength in a wide wavelength range of visible light, there is known a laminated quarter-wave plate in which a quarter-wave plate and a half-wave plate produced by uniaxial stretching are laminated on each other so that directions of in-plane slow axes of these plates intersect each other. For example, the laminated quarter-wave plate is widely used for the purpose of anti-reflection of a liquid-crystal display device (hereinafter referred to as xe2x80x9cLCDxe2x80x9d).
A TFT (Thin Film Transfer) drive type twisted nematic (TN) LCD is widely used in a notebook type personal computer, a monitor, etc. The TN-LCD has a disadvantage in that the viewing angle thereof is narrow. A VA- or IPS-LCD capable of providing a wide viewing angle have been developed and begun to be popularized for monitor use. The VA- or ISP-LCD, however, needs backlight electric power because the VA- or ISP-LCD is lower in luminance than the TN-LCD. Moreover, the VA- or ISP-LCD has been not applied to a notebook type personal computer requiring low electric power consumption.
On the other hand, it is known that frontal luminance of a multi-domain VA-LCD is improved when the laminated quarter-wave plate is disposed in one interlayer between a liquid-crystal cell and a polarizer while a laminated quarter-wave plate capable of providing circularly polarized light of reverse rotation is disposed in another interlayer. In this method, it is however difficult to obtain a wide viewing angle. This problem can be solved by the related art when a negative uniaxial phase retarder produced by biaxial stretching and a polarizer are laminated on each other. There is, however, a disadvantage in that the resulting film is made thick because a large number of plates must be laminated as well as production efficiency is made low because a large number of laminating steps is required.
To solve the problems in the related art, on object of the invention is to provide a quarter-wave plate or a circularly polarizing plate adapted to compensation for birefringence, a liquid-crystal display device using the same and a method for producing the same.
In order to solve the object, according to the invention, there is provided a laminated quarter-wave plate having: a laminate of a quarter-wave plate and a half-wave plate, wherein: the quarter-wave plate and the half-wave plate are laminated on each other so that directions of in-plane slow axes intersect each other; and each of the quarter-wave plate and the half-wave plate satisfies a relation Nz=(nxxe2x88x92nz)/(nxxe2x88x92ny) greater than 1.05 in which nx and ny are in-plane main refractive indices, and nz is a thicknesswise refractive index. Further, according to the invention, there is provided a circularly polarizing plate having: a laminate of a laminated quarter-wave plate defined above and a polarizer.
Further, according to the invention, there is provided a pressure sensitive adhesive agent-including laminated quarter-wave plate having: a laminated quarter-wave plate defined above; and a pressure sensitive adhesive layer provided on at least one of opposite surfaces of the laminated quarter-wave plate.
Further, according to the invention, there is provided a pressure sensitive adhesive agent-including circularly polarizing plate having: a circularly polarizing plate defined above; and a pressure sensitive adhesive layer provided on at least one of opposite surfaces of the circularly polarizing plate.
Further, according to the invention, there is provided a liquid-crystal display device having: a liquid-crystal cell; and a laminated quarter-wave plate or circularly polarizing plate defined above, or a pressure sensitive adhesive agent-including laminated quarter-wave plate or circularly polarizing plate defined above and disposed on at least one of opposite surfaces of the liquid-crystal cell.
Next, according to the invention, there is provided a method of producing a phase retarder (such as a quarter-wave plate or a half-wave plate) satisfying a relation Nz=(nxxe2x88x92nz)/(nxxe2x88x92ny) greater than 1.05 in which nx and ny are in-plane main refractive indices, and nz is a thicknesswise refractive index, the method having the step of: stretching a transparent polymer film with a thickness of 5 to 500 xcexcm by one of tenter lateral stretching and biaxial stretching.
Features and advantages of the invention will be evident from the following detailed description of the preferred embodiments described in conjunction with the attached drawings.